This invention relates to an internal combustion engine fuel control system.
It has been observed that the roughness of running of an internal combustion engine increases as under fueling increases. It has already been proposed to measure engine roughness by comparing the times taken for the engine shaft to travel through a fixed angle at different angular positions of the shaft. The difference between these times is representative of the roughness and a circuit has already been proposed which is intended to produce an electrical output signal dependant on the magnitude of the speed fluctuation of the engine in relation to the speed thereof, i.e. the output signal will be the same at twice the existing speed if the magnitude of the speed fluctuations is also doubled.
When applying a roughness sensor of this general type to a fuel control system, however, it is found that the use of such a speed-normalised roughness signal is not satisfactory, because the level of roughness which is tolerable at high speed is not tolerable at low speed.